1. Field of Invention
This invention relates to wireless communications systems. Specifically, the present invention relates to systems and methods for facilitating load sharing between frequencies in wireless communications networks employing cells with multiple frequencies.
2. Description of the Related Art
Wireless communications systems are employed in a variety of demanding applications including Internet, faxing, and voice communications applications. Such applications require cost-effective, reliable service. As demand for wireless services expands along with new applications, wireless communications systems must adapt to efficiently accommodate increased network usage.
Systems for efficiently handling increased wireless network usage are particularly desirable in new digital wireless communications systems, such as code division multiple access (CDMA) telecommunications systems. A CDMA system often includes a plurality of mobile stations (e.g. cellular telephones, mobile units, wireless telephones, or mobile phones) in communication with one or more base station transceiver subsystems (BTS's). Signals transmitted by the mobile stations are received by a BTS and often relayed to a mobile switching center (MSC) having a base station controller (BSC). The MSC, in turn, routes the signal to a public switched telephone network (PSTN), to a Packet Data Network (PDN)—internet, or to another mobile station via a BTS. Similarly, a signal may be transmitted from the public switched telephone network or PDN to a mobile station via a base station or BTS and an MSC.
Each BTS governs a cell corresponding to a region within which a mobile station may communicate with the BTS. Calls within cells are routed from mobile stations to and from a telecommunications network via an associated BTS and an MSC. The coverage area of a typical cellular telecommunications system is divided into several cells. Different communications resources, such as frequencies, are often allocated to each cell to increase communications system resources. When a mobile station moves from a first cell to a second cell, a handoff is performed to assign new system resources associated with the second cell to the mobile station.
A BTS routes calls between mobile stations within a predetermined geographic area, i.e., cell governed by the BTS, and to and from an MSC and a BSC. The MSC and BSC facilitate the routing of calls between BTS's and between the wireless communications network and the PSTN or internet, which is also called the wireline network or the landline network.
A BSC or MSC is often associated with a particular geographic area comprising one or more cells and often includes various components such as a selector bank subsystem (SBS) and radio link manager (RLM) to facilitate the allocation of network resources between voice or data calls and other network functions. Network resources may include available hardware resources, such as channel elements, handling resources, such as available Walsh codes, and air link resources, such as available transmit power.
Wireless communications systems must efficiently use network resources to accommodate increased network usage. Wireless networks often employ additional frequencies in the system operating frequency band to accommodate additional users. In such systems, each additional frequency is typically accompanied by additional hardware to accommodate users employing the additional frequencies.
When a user turns on a wireless phone operating within the network, the user is assigned to one of the available frequencies in the coverage area in which the user is operating based on a pseudo random function known as a hash function. The hash function is based on a user identification number. Once on a call, the user is assigned to a given frequency, known as the access frequency, the user typically stays assigned to that frequency until the user reaches the boundary of the frequency coverage area, and is handed off to another frequency.
Unfortunately, this method of allocating wireless frequency resources among users does not efficiently account for the movement of users, overlapping frequency coverage areas, nor the position of users within the overall wireless network coverage area. Consequently, some frequencies may become overloaded, resulting in dropped calls, while other available frequencies remain under-utilized. For example, a coverage area associated with a frequency f1 may contain a smaller overlapping coverage area having an additional available frequency f2. When a user is assigned to f1 and moves into the overlapping coverage area where f1 and f2 are available, the user remains assigned to f1 even if f1 is congested relative to f2. When f1 is overloaded, calls are often dropped or blocked to alleviate the overload condition, resulting in reduced service reliability. Alternatively, additional expensive hardware is added to accommodate additional users on f1, while the hardware associated with f2 remains under-utilized. Such load imbalances are undesirable and represent inefficient use of network resources. In addition to reduced network reliability, these load imbalances may result in increased costs as network administrators add expensive hardware to accommodate the additional users.
Hence, a need exists in the art for a system and method that efficiently balances the load between frequencies in a wireless communications network having coverage areas with multiple frequencies, thereby minimizing hardware requirements and maximizing capacity per frequency. There exists a further need for a system that efficiently accounts for the movement of users and the position of users relative to overlapping frequency coverage areas and facilitates the sharing of hardware resources across frequencies.